The present invention relates to a novel polyamide epoxy ester resin, a process for the preparation thereof, and a coating composition comprising the polyamide epoxy ester resin.
The polyamide epoxy ester resin of the present invention is useful as a coating resin to be applied where strong adhesiveness, greater pliability, and high corrosion resistance are required. The resin of the present invention is especially useful for coating a steel sheet coil to be subjected to draw-forming or shearing, and particularly for coating the inner surface of a can such as a food can or beverage can.
In the canned products industry, producers all over the world tend to follow Title 21 of the Code of Federal Regulation (23 CFR) regulation by the Food and Drug Administration (FDA) of the United States as the standard for inner surface paints for food cans and beverage cans. For epoxy resin coating compositions, usable curing agents, catalysts and additives are strictly restricted by 21 CFR 175.300 (b) (3) (viii).
Heretofore, high-molecular-weight epoxy resins esterified with a vegetable oil fatty acid have been used for improving the pliability and processability of inner surface coatings of cans. However, these resins have an unsatisfactory workability and pliability.
Modification of epoxy resins with a polymerized fatty acid (dimer acid) gives an excellent curing characteristic, workability, pliability and adhesiveness. This polymerized fatty acid itself is not listed as an epoxy resin additive in 21 CFR. On the other hand, a polyamide obtained from a dimer acid and a diamine is listed in 21 CFR 175.300 (b)(3)(viii), and thus a polyamide amine is used as a curing agent. The polyamide amine, however, has a poor compatibility with an epoxy resin and the pot life of the obtained using the epoxy resin paint is short. Accordingly, the polyamide is currently used as an ingredient for a two-pack type paint.
An object of the present invention is to provide a modified epoxy resin for a coating composition prepared from materials listed in regulation 21 CFR 175.300 (b)(3)(viii), which has a coating performance equivalent to, or better than, that of a dimer acid-modified epoxy resin.
Another object of the present invention is to provide a modified epoxy resin which has paint stability and curing characteristics equivalent to, or better than, those of a conventional epoxy resin.
Still another object of the present invention is to provide a process for the preparation of such a modified epoxy resin and a coating composition comprising such a resin.